Cordless telephones are made up of a base unit, which is traditionally connected to a telephone wall outlet and to an AC power outlet, and is thus fixed in location, and a portable handset. The handset is normally in one of two positions. In a first position, the handset is coupled to the base unit, such as by being cradled thereto, and is normally receiving charging power from the base unit through a set of charge contacts. When in this position, the telephone is in an on-hook condition, i.e., is not connected to the central office or to another telephone or otherwise engaged in telephony activities.
In a second position, the handset is de-coupled from the base unit and is capable of communicating with the base unit through RF communications. When in this position, the telephone may be in either an on-hook condition or an off-hook condition. When in the off-hook condition, a user engages in telephony activities by using the handset. The handset maintains an RF link with the base unit, and the base unit establishes wired connection to the central office and the public switched telephone network (or to an internet service provider based network or any other form of network).
The major advantage of cordless telephones, when compared to traditional wired telephones, is that cordless telephones do not require the user to remain at one given location while engaged in telephony activities. Instead, the user is able to roam within range of the base unit, and as long as the handset is within range, the user can engage in telephony activities such as initiating outgoing telephone calls and receiving incoming telephone calls. Typically, as cordless telephone technology advances, the range of the RF link between the base and handset continues to increase. This is partly due to the use of higher powered RF frequencies which are allowed due to the use of digital, as opposed to analog, communication techniques, enabling more advanced digital signal processing features, such as frequency hopping, spread spectrum, forward error correction, etc.
A drawback of cordless telephones is that the capability to roam with the handset also creates the opportunity for a user to misplace the handset. For example, a user may roam within the user's home while engaged in a telephone conversation, and when the conversation is complete the user may simply put the handset down in any convenient spot. If the user becomes otherwise distracted, the user may forget where the user placed the handset when the user later desires to place a new outgoing telephone call. To address this problem, cordless telephones have developed a feature, typically referred to as the "page" or "handset locator" feature, whereby the user presses a page button on the base unit to cause the handset to provide an audible signal, typically a short three-"beep" signal.
A drawback of conventional page signals is that they are the same regardless of the environmental conditions. As the allowable range between the base and handset gets bigger, this can yield a problematic situation wherein the user cannot effectively employ the page feature since the user either cannot hear the short audible signal, or cannot accurately determine the source of the audible signal before it terminates. There is therefore a need for a cordless telephone with an adaptive paging feature to adjust to the conditions so that a user can effectively locate a misplaced handset.